In an open shed Jacquard machine of this kind two hooks are joined at the bottom end over a common pulley, and the hooks, depending on the control means used, can be coupled usually with two lifting knives which constantly move in opposite directions, whereby the pulley and therefore the warp thread connected thereto, are given a controlled lifting movement. Open shed Jacquard machines of this kind have become less important with the development of Jacquard machines with single hooks which do not require a pulley system and can be controlled by means of punched cards.
The inherent advantages of the open shed Jacquard machine in comparison to the other Jacquard machines again become significant if electronic data processing can be used to control Jacquard machines. This is the case if electrically controllable systems such as magnets can be used for the control. An early attempt is described in DE-OS 22 04 815 in which for each hook a hook element is provided as an essential intermediate member which is held resiliently in an arresting position and which, by energizing a respective electromagnet, is moved out of the arresting position and pulled across the air gap towards the electromagnet. This hook control device is obviously very complicated and therefore susceptible to trouble and in addition requires a considerable amount of space.
A further development is described in GB-OS 20 47 755. In this known control device, on which the present invention is based, a single magnet is arranged between the two hooks of a pair of hooks whereby arresting only occurs in the upper shed position when the magnet is energized in this position and attracts the hook across the substantial air gap. In an alternative embodiment, for each hook a hook element is attached to the carrier of the single magnet as an intermediate member, and the nebs of these hook elements must be moved out of the path of movement of the hook when the magnet is energized and moved across a likewise substantial air gap to abut against the magnet yoke.
Owing to the fact that when the magnet is energized the movable elements (hook or intermediate member) must be moved over a substantial air gap, which depends on the design and cannot be defined exactly, the problem is not only that the energy requirements are considerable. In addition, considerable efforts are needed for shielding neighbouring magnets, and there is also the danger that when de-energizing the magnet a controlled hook or a controlled intermediate member remains adhering to the magnet or its pole, resulting in defective control so that reliable operation is not ensured. In addition the known system has the disadvantage that it can only operate exclusively in the upper shed position whereby it is only possible to hook and unhook the elements under high tension which results in great stresses and great wear. This disadvantage is particularly serious when an adhering hook is suddenly released from the electromagnet and moves at great speed through the Jacquard machine until it collides with great force with a knife or the bottom board. This can easily lead to damage and the hook can even be destroyed. Finally, many structural elements are necessary, which is an obstacle to a compact arrangement which is simple to assemble.